1. Field of the Invention
The present invention relates to surface-mounted antennas capable of transmitting and receiving the signals of different frequency bands and wireless devices incorporating the same.
2. Description of the Related Art
Recently, there has been a demand for wireless devices on the market, in which a single wireless device such as a mobile phone needs to be adaptable to multi-bands for a plurality of applications, for example, the global system for mobile communications (GSM) and the digital cellular system (DCS), the personal digital cellular (PDC) and the personal handyphone system (PHS), and the like. In order to meet the demand, there are provided various antennas. In these cases, the signals of different frequency bands can be transmitted and received by using only a single antenna.
Such an antenna, however, has many problems in handling multi-bands. Particularly, in required multiple frequency bands, in a region closer to the high-frequency side, the frequency bandwidth tends to be narrower. As a result, it is difficult to obtain bandwidths allocated to the applications. In addition, it is extremely difficult to control the frequency bandwidths independently from each other. These are critical problems to be solved.
In view of the foregoing problems, it is an object of the present invention to provide a multi-band surface-mounted antenna. The signals of different frequency bands can be transmitted and received by the single antenna. Additionally, the broadening of frequency bands can be easily made, and particularly, the frequency bandwidths can be controlled independently from each other. Furthermore, it is another object of the invention to provide a wireless device incorporating the multi-band surface-mounted antenna.
In order to accomplish the above objects, according to a first aspect of the present invention, there is provided a surface-mounted antenna including a dielectric base member, a feeding element formed by extending a radiation electrode from a feeding terminal on the dielectric base member, and a non-feeding element formed by extending a radiation electrode from a ground terminal on the dielectric base member. In this arrangement, the feeding element and the non-feeding element are arranged via a distance therebetween. In addition, at least one of the feeding element and the non-feeding element is a branched element formed by extending a plurality of radiation electrodes branched from the feeding-terminal side or the ground-terminal side via a distance therebetween.
In this surface-mounted antenna, the plurality of radiation electrodes forming the branched element may have different fundamental-wave resonance frequencies.
In addition, in the surface-mounted antenna, the plurality of radiation electrodes forming the branched element may be extended from one of the feeding-terminal side and the ground-terminal side in directions in which the distance between the radiation electrodes is expanded.
Furthermore, in the surface-mounted antenna, at least one of the plurality of radiation electrodes forming the feeding element and the non-feeding element may locally include at least one of a fundamental-wave controlling unit for controlling a fundamental-wave resonance frequency and a harmonic controlling unit for controlling a harmonic resonance frequency.
In this surface-mounted antenna, the fundamental wave controlling unit may be locally disposed in a fundamental-wave maximum resonance current region including a maximum current portion at which a fundamental-wave resonance current reaches a maximum on a current path of the radiation electrode. In addition, the harmonic controlling unit may be locally disposed in a harmonic maximum resonance current region including a maximum current portion at which a harmonic resonance current reaches a maximum on the current path of the radiation electrode.
In addition, on the feeding element, there may be alternately arranged a region of a small current length per unit length and a region of a large current length per unit length along the current path.
In addition, in the surface-mounted antenna, at least one of the branched radiation electrodes of one of the feeding element and the non-feeding element may perform combined resonance with a radiation electrode of the remaining element.
In addition, in the surface-mounted antenna, electric power may be supplied to the feeding terminal of the feeding element by capacitive coupling.
According to a second aspect of the present invention, there is provided a wireless device including the surface-mounted antenna described above.
In this specification, of the plurality of resonance waves of the radiation electrodes, the resonance wave having the lowest resonance frequency is defined as the fundamental wave, and the resonance waves having resonance frequencies higher than that of the fundamental wave are defined as the harmonics. In addition, a state in which there are two or more resonance points within one frequency band is defined as combined resonance.
In the above structure, at least the three radiation electrodes are formed on a surface of the dielectric base member so that the antenna is easily adaptable to multi-bands. Moreover, by setting the current-vector directions of the radiation electrodes and the distances between the radiation electrodes according to needs, the resonance waves of the radiation electrodes can be controlled independently from each other. Thus, for example, only one frequency band of required frequency bands is selected to set in a multi-resonance state so that broadening of the used frequency band can be very easily achieved.